1. Technical Field of the Invention
This invention relates generally to HVAC zone control systems for retrofit, and specifically to a remote controlled vehicle to assist in threading string, air tubes, and wires through concealed HVAC duct systems.
2. Background Art
Most zone control systems for HVAC systems use electromechanical dampers to selectively control the airflow through portion of the trunk and duct system. Installation of these zone systems requires access to the ducts at multiple locations so that the dampers can be installed. Although the duct is accessible for damper installation, there may be no easily accessible path to run control wires from the damper to the control system because portions of the duct may be enclosed in walls, floors, or ceilings. However the duct system does provide a clear path provided the zone control equipment is located near the HVAC equipment. The existing ductwork can be used as a conduit for running the control wires, but this requires a practical method for threading the wire from the damper to the HVAC equipment.
U.S. Pat. No. 6,786,473 issued Sep. 7, 2004 to Alles, U.S. Pat. No. 6,893,889 issued Jan. 10, 2004 to Alles, U.S. Pat. No. 6,997,390 issued Feb. 14, 2006 to Alles, U.S. Pat. No. 7,062,830 issued Jun. 20, 2006 to Alles, U.S. Pat. No. 7,162,884 issued Jan. 16, 2007 to Alles, U.S. Pat. No. 7,188,779 issued Mar. 13, 2007 to Alles, and U.S. Pat. No. 7,392,661 issued Jul. 1, 2008 to Alles, describes various aspects of a HVAC zone climate control system that uses inflatable bladders. The present invention is by the same inventor and is designed to assist in the installation of this system.
The system invented by Alles has multiple inflatable bladders installed in the supply ducts such that the airflow to each vent can be separately controlled by inflating or deflating the bladder in its supply duct. Each bladder is connected to an air tube that is routed through the duct and trunk system back to a set of centrally located computer controlled air valves that can separately inflate or deflate each bladder. Based on temperature readings from each room and the desired temperatures set for each room, the system controls the heating, cooling, and circulation equipment and inflates or deflates the bladders so that the conditioned air is directed where needed to maintain the set temperatures in each room.
U.S. Pat. No. 7,062,830 issued Jun. 20, 2006 to Alles describes a method of installing the air tubes. This method uses air flow from the vent toward the HVAC equipment to pull a parachute and thin string from the vent to the HVAC equipment. At the HVAC equipment, an air tube is connected to a string and the string is pulled toward the vent until the air tube reaches the vent. This method requires all vents but one be blocked so that all of the airflow generated by a blower at the HVAC system comes from one vent. This method works well for many duct systems and specific duct paths. However, this method does not work well for some duct systems and specific duct paths.
Excessive duct leakage can prevent this method from working. With all vents sealed but one, all of the airflow generated by the blower should flow through the one open vent. However, the airflow can also come for all of the leaks in the duct system. If the leakage is excessive, there is insufficient airflow at the vent to inflate and pull the parachute.
Small supply ducts at the vent in the range of 4″ to 6″ in diameter can prevent this method from working even with strong airflow. In a small vent, a large portion of the parachute is in contact with the walls of the duct creating a large drag, and screws or sharp edges are likely to snag the parachute. In addition, the airflow in the small cross-section area produces only a small force on the parachute. Increasing the air flow to increase the pulling force also increases the drag since parts of the parachute are pushed harder against the duct walls. The combination of high drag and small force makes it difficult for the parachute to pass through the duct.
If a smaller parachute is used for smaller ducts, it is often easier for the parachute to pass through the duct. However, the small duct eventually connects to a larger duct or main supply trunk. As the duct cross-section increases, the air velocity decrease and the small parachute can not product enough force to pull the string to the HVAC equipment.
In some duct networks with long duct runs with many turns, the resistance between the string and the duct walls become excessive as the length of the string being pulled increases. The force generated by the parachute is not sufficient to overcome the string pulling friction.
Patent application 12240570 discloses a method that overcomes some of these limitations. It discloses methods for propelling a string through a small duct to a larger trunk and separate methods for retrieving the string in the trunk and pulling it to an access cut into the trunk near the HVAC equipment.
A specially adapted remote controlled vehicle can be used to capture and retrieve a string in a trunk. Small remote controlled vehicles are produced in various sizes and styles for the toy and hobbyist market. Their design and function are understood by those skilled in the art. However, they are not adapted for use in HVAC trunks and for the purpose of capturing a string or parachute.
U.S. Pat. No. 5,020,188 issued Jun. 4, 1991 and U.S. Pat. No. 5,072,487 issued Dec. 17, 1991 to Walton discloses a vehicle adapted for traveling inside HVAC ducts and spraying liquids to clean the ducts. It was guided by the duct wall and had no provisions for remote steering. It did not provide video camera and display for showing the inside of the ducts as it traveled.
U.S. Pat. No. 5,317,782 issued Jun. 7, 1994 to Matsuura discloses a remote controlled tracked vehicle adapted for traveling inside HVAC duct and cleaning ducts. It included a video camera fixed to the body of the vehicle and a remote display for viewing the image. It also included a swiveling air jet for blowing debris from the duct wall. The vehicle followed the walls of the duct and provided no method for remote controlled steering.
U.S. Pat. No. 5,377,381 issued Jan. 3, 1995 to Wilson describes a vehicle adapted for traveling inside HVAC ducts and cleaning the ducts. It had specialized tools for spraying and brushing. It did not have the ability make controlled turns since it was designed to be guided by the duct walls. It did not provide video camera and display for showing the inside of the ducts as it traveled.
U.S. Pat. No. 5,528,789 issued Jun. 25, 1996 to Rostamo discloses a remote controlled tracked vehicle adapted for cleaning ducts. The vehicle could be steered remotely and could be maneuvered independent of the duct walls. It included a video camera fixed to the body of the vehicle with a lighting system so the inside of the ducts could be viewed on a remote display. It also included a rotating brush powered by air pressure that could be raised and lowered by remote control.
The remote controlled vehicles of the previous art for use in HVAC duct were adapted for cleaning. Thus they were relatively large to support the weight and stress caused by the cleaning apparatus and process. They required a compressed air source to power the cleaning apparatus. They were too large to fit in many trunks routinely used in residential HVAC systems. They did not have a moveable tool adapted to capture string or a moveable video camera adapted to searching for string.